Before I send the board off to Clive at Coin-Op Cauldron, I thought I would "ask the forum".

Customer brought in an auction-buy Dr. Who, which had been on route for many years based on permit stickers and overall condition. Asked me to "get it playing".

Customer told me the game had been working, but judging by the coils and dis-assembled parts hanging under the playfield, missings pieces, etc, I wasn't so sure.

Power supply seemed to be outputting the correct voltages, so I plugged it in with the customer still present. I'm glad I did, because when I switched on the power, its as if a mini-flash-bang went off on the sound board!

After the smoke cleared, I determined that C28 went all 'splodey on us. What's strange is even though the cap was blown clean in two, I STILL GET CONTINUITY across the legs of the cap! I'm wondering if the traces somehow got shorted in the "explosion"? Or maybe the short CAUSED the explosion.

Another question is, IS THIS EVEN THE RIGHT BOARD? Dr. Who manual calls for a 12738-20006 sound board, but the board in the game is a 12742-20006. Are these interchangeable?

Any and all thoughts are welcome.

20180419_144440 (resized).jpg

20180419_141915-1 (resized).jpg

Thanks for the reply Coyote. As you can see in the photos I added, the sound board has 12742-20006 on it. Its the white sticker in the middle of the board.

Didn't know tant caps liked to blow like that. Quite exciting when they do!

Dumbass, its members like you that keep me coming back to Pinside! Thanks for adding to the discussion. I will do as you suggest.

I put the board back into the game to test voltages AND THE DAMN THING STILL WORKS! There is a distinct "hiss" in the background, but the board still works 100%! Obviously I won't leave it this way, but I found it shocking (no pun intended) that it still functions!

BK, great advice. I've done plenty of minor board repair, but I never thought about this before. Moving forward, procedures will be different. Seems like we have to learn the hard way sometimes!

Thanks Brian. It's always good to hear from someone who has been through the exact same issue! I have a large supply of "normal" capacitors, I'm tempted to use them, albeit with a higher rating, instead of ordering the tantalum caps.

Ok, now I'm a bit confused. It appears that audio board connector J501 brings in 20VAC through pin 1, with a trace that leads directly to the tantalum cap that exploded. My confusion is on the fact that it is my understanding that you never use polarized caps in an AC circuit, only "NP" or non-polarized. But the specs on the tant cap in the manual doesn't have an NP in the specs, making me think its just a normal polarized cap.

Looking at Dumbass's picture, it appears there is a small "+" sign on the right side of the blown cap. This would indicate polarized.

Brian, what exact cap did you buy to do the repair? Can you post a link?

Alright, I looked a the remains of the blown cap and it is polarized. Positive toward the input from J501. I've also come to understand that two polarized caps, fitted in parallel with opposite polarity, creates a "non-polarized" cap. That may be what's happening here.

Thanks for all the support guys! I replaced the tant cap with an oversized regular cap, and all is well! Sound card works 100%, and the background "hiss" is gone. Just nice, clean crisp sounds emanating from the speakers!